Pneumatic tire having a component containing high trans styrene-butadiene rubber

ABSTRACT

The invention is directed to a pneumatic tire having at least one component comprising a vulcanizable rubber composition, wherein the vulcanizable rubber composition comprises, based on 100 parts by weight of elastomer (phr), from about 30 to 100 phr of high trans random SBR, and from about zero to about 70 phr of at least one additional elastomer, wherein the high trans random SBR comprises from about 3 to about 30 percent by weight of styrene.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of co-pending Ser. No.10/224,984, filed Aug. 21, 2002.

BACKGROUND OF THE INVENTION

[0002] It is highly desirable for tires to have good wet skidresistance, low rolling resistance and good wear characteristics. It hastraditionally been very difficult to improve a tire's wearcharacteristics without sacrificing its wet skid resistance and tractioncharacteristics. These properties depend, to a great extent, on thedynamic viscoelastic properties of the rubbers utilized in making thetire.

[0003] In order to reduce the rolling resistance and to improve thetreadwear characteristics of tires, rubbers having a high rebound havetraditionally been utilized in making tire tread rubber compounds. Onthe other hand, in order to increase the wet skid resistance of a tire,rubbers which undergo a large energy loss have generally been utilizedin the tire's tread. In order to balance these two viscoelasticallyinconsistent properties, mixtures of various types of synthetic andnatural rubber are normally utilized in tire treads. For instance,various mixtures of styrene-butadiene rubber and polybutadiene rubberare commonly used as a rubbery material for automobile tire treads.

[0004] U.S. Pat. No. 6,103,842 and U.S. application Ser. No. 10/124,006,now U.S. Pat. No. 6,627,715, disclose processes and catalyst systems forthe copolymerization of 1,3-butadiene monomer and styrene monomer into astyrene-butadiene copolymer having a high trans-1,4-polybutadienecontent and having a random distribution of repeat units which arederived from styrene. It is also therein disclosed thatstyrene-butadiene rubber made utilizing the catalyst system andtechniques therein may be used in the preparation of tire tread rubbercompounds which exhibit improved wear characteristics. What is notdisclosed is that superior wear characteristics may be obtained using alow styrene content in the high trans random SBR.

SUMMARY OF THE INVENTION

[0005] The current invention is directed to a pneumatic tire having atleast one component comprising a high trans solution styrene-butadienerubber (HTSBR) with a random distribution of repeat units which arederived from styrene. The invention is based on the highly surprisingand unexpected discovery that a desirable balance of properties may berealized by using a HTSBR with a low styrene content.

[0006] It is then an object of the present invention to provide apneumatic tire having at least one component comprising a vulcanizablerubber composition, wherein the vulcanizable rubber compositioncomprises, based on 100 parts by weight of elastomer (phr), from about30 to 100 phr of high trans random SBR, and from about zero to about 70phr of at least one additional elastomer, wherein the high trans randomSBR comprises from about 3 to about 30 percent by weight of styrene.

DESCRIPTION OF THE INVENTION

[0007] The pneumatic tire of the present invention has at least onecomponent comprising a high trans solution styrene-butadiene rubberHTSBR. By HTSBR, it is meant an SBR produced by a solution method andhaving a percentage of trans-1,4-butadiene conformation in thepolybutadiene segments of the polymer of greater than 60 percent byweight. Alternatively, suitable HTSBR may have a percentage oftrans-1,4-butadiene conformation in the polybutadiene segments of thepolymer of greater than 70 percent by weight. Suitable HTSBR may containfrom about 3 to about 30 percent by weight of styrene. Alternatively,suitable HTSBR may contain from about 3 to about 20 percent by weight ofstyrene. Alternatively, suitable HTSBR may contain from about 3 to about10 percent by weight of styrene.

[0008] Suitable HTSBR may be made by any of the suitable solutionpolymerization methods as are known in the art. In one embodiment,suitable HTSBR may be made using the methods of U.S. Pat. No. 6,103,842.In another embodiment, suitable HTSBR may be made using the methods ofU.S. application Ser. No. 10/124,006, now U.S. Pat. No. 6,627,715.Styrene-butadiene rubbers so made may contain from about 2 weightpercent to about 50 weight percent styrene and from about 50 weightpercent to about 98 weight percent 1,3-butadiene. However, in somecases, the amount of styrene included will be as low as about 1 weightpercent. In one embodiment of the present invention, suitablestyrene-butadiene rubber so made will contain from about 3 weightpercent to about 30 weight percent styrene and from about 70 weightpercent to about 97 weight percent 1,3-butadiene. In another embodiment,suitable styrene-butadiene rubber will contain from about 3 weightpercent to about 20 weight percent styrene and from about 80 weightpercent to about 97 weight percent 1,3-butadiene. In another embodiment,suitable styrene-butadiene rubber will contain from about 3 weightpercent to about 10 weight percent styrene and from about 90 weightpercent to about 97 weight percent 1,3-butadiene. Thesestyrene-butadiene rubbers typically have a melting point which is withinthe range of about below 44° C. Higher styrene content HTSBR may exhibitno melting point.

[0009] The styrene-butadiene rubber will typically have a glasstransition temperature in a range of from about −55° C. to about −85°C.; alternatively from about −65° C. to about −85° C.

[0010] In suitable styrene-butadiene rubbers containing less than about30 weight percent bound styrene, the distribution of repeat unitsderived from styrene and butadiene is essentially random. The term“random” as used herein means that less than 10 percent of the totalquantity of repeat units derived from styrene are in blocks containingmore than five styrene repeat units. In other words, more than 90percent of the repeat units derived from styrene are in blockscontaining five or fewer repeat units. About 20% of the repeat unitsderived from styrene will be in blocks containing only one styrenerepeat unit. Such blocks containing one styrene repeat unit are bound onboth sides by repeat units which are derived from 1,3-butadiene.

[0011] In suitable styrene-butadiene rubbers containing less than about20 weight percent bound styrene, less than 4 percent of the totalquantity of repeat units derived from styrene are in blocks containingfive or more styrene repeat units. In other words, more than 96 percentof the repeat units derived from styrene are in blocks containing lessthan five repeat units. In such styrene-butadiene rubbers, over 25percent of repeat units derived from styrene will be in blockscontaining only one styrene repeat unit, over 60 percent of the repeatunits derived from styrene will be in blocks containing less than 3repeat units and over 90 percent of the repeat units derived fromstyrene will be in blocks containing 4 or fewer repeat units.

[0012] In suitable styrene-butadiene rubbers containing less than about10 weight percent bound styrene, less than 1 percent of the totalquantity of repeat units derived from styrene are in blocks containing 5or more styrene repeat units. In other words, more than 99 percent ofthe repeat units derived from styrene are in blocks containing 4 or lessrepeat units. In such styrene-butadiene rubbers, at least about 50percent of repeat units derived from styrene will be in blockscontaining only one styrene repeat unit and over about 85 percent of therepeat units derived from styrene will be in blocks containing less than3 repeat units.

[0013] Suitable styrene-butadiene copolymers also have a consistentcomposition throughout their polymer chains. In other words, the styrenecontent of the polymer will be the same from the beginning to the end ofthe polymer chain. No segments of at least 100 repeat units within thepolymer will have a styrene content which differs from the total styrenecontent of the polymer by more than 10 percent. Such styrene-butadienecopolymers will typically contain no segments having a length of atleast 100 repeat units which have a styrene content which differs fromthe total styrene content of the polymer by more than about 5 percent.

[0014] In the broadest embodiment, suitable HTSBR may be made by any ofthe suitable solution polymerization methods as are known in the art. Inone embodiment, suitable HTSBR may be produced using a process as taughtin U.S. application Ser. No. 10/124,006, now U.S. Pat. No. 6,627,715,fully incorporated herein by reference, that comprises copolymerizingstyrene and 1,3-butadiene in an organic solvent in the presence of acatalyst system that is comprised of

[0015] (A) an organolithium compound,

[0016] (B) a group IIa metal salt selected from the group consisting ofgroup IIa metal salts of amino glycols and group IIa metal salts ofglycol ethers, and

[0017] (C) an organometallic compound selected from the group consistingof organoaluminum compounds and organomagnesium compounds.

[0018] In another embodiment, suitable HTSBR may be produced using aprocess as taught in U.S. Pat. No. 6,103,842, fully incorporated hereinby reference, that comprises copolymerizing styrene and 1,3-butadieneunder isothermal conditions in an organic solvent in the presence of acatalyst system which consists essentially of

[0019] (A) an organolithium compound,

[0020] (B) a barium alkoxide and

[0021] (C) a lithium alkoxide.

[0022] In one embodiment, the pneumatic tire of the present inventionmay include a component comprising between about 30 and about 100 partsby weight of HTSBR. The component may also include between zero and upto 70 parts by weight of other elastomers as are known in the art, tomake up a total 100 parts by weight of elastomer. In another embodiment,the pneumatic tire of the present invention may include a componentcomprising between about 50 and about 100 parts by weight of HTSBR. Thecomponent may also include between zero and up to 50 parts by weight ofother elastomers as are known in the art, to make up a total 100 partsby weight of elastomer.

[0023] Other elastomers that may be used along with the HTSBR mayinclude various general purpose elastomers as are known in the art. Thephrase “rubber or elastomer containing olefinic unsaturation” isintended to include both natural rubber and its various raw and reclaimforms as well as various synthetic rubbers. In the description of thisinvention, the terms “rubber” and “elastomer” may be usedinterchangeably, unless otherwise prescribed. The terms “rubbercomposition”, “compounded rubber” and “rubber compound” are usedinterchangeably to refer to rubber which has been blended or mixed withvarious ingredients and materials and such terms are well known to thosehaving skill in the rubber mixing or rubber compounding art.Representative synthetic polymers are the homopolymerization products ofbutadiene and its homologues and derivatives, for example,methylbutadiene, dimethylbutadiene and pentadiene as well as copolymerssuch as those formed from butadiene or its homologues or derivativeswith other unsaturated monomers. Among the latter are acetylenes, forexample, vinyl acetylene; olefins, for example, isobutylene, whichcopolymerizes with isoprene to form butyl rubber; vinyl compounds, forexample, acrylic acid, acrylonitrile (which polymerize with butadiene toform NBR), methacrylic acid and styrene, the latter compoundpolymerizing with butadiene to form SBR, as well as vinyl esters andvarious unsaturated aldehydes, ketones and ethers, e.g., acrolein,methyl isopropenyl ketone and vinylethyl ether. Specific examples ofsynthetic rubbers include neoprene (polychloroprene), polybutadiene(including cis-1,4-polybutadiene), polyisoprene (includingcis-1,4-polyisoprene), butyl rubber, halobutyl rubber such aschlorobutyl rubber or bromobutyl rubber, styrene/isoprene/butadienerubber, copolymers of 1,3-butadiene or isoprene with monomers such asstyrene, acrylonitrile and methyl methacrylate, as well asethylene/propylene terpolymers, also known as ethylene/propylene/dienemonomer (EPDM), and in particular, ethylene/propylene/dicyclopentadieneterpolymers. Additional examples of rubbers which may be used include acarboxylated rubber, silicon-coupled and tin-coupled star-branchedpolymers. The preferred rubber or elastomers are polybutadiene, SBR, andnatural rubber.

[0024] In one aspect the rubber to be combined with the HTSBR ispreferably one or more diene based rubbers. For example, one or morerubbers is preferred such as cis 1,4-polyisoprene rubber (natural orsynthetic, although natural is preferred), 3,4-polyisoprene rubber,styrene/isoprene/butadiene rubber, emulsion and solution polymerizationderived styrene/butadiene rubbers, cis 1,4-polybutadiene rubbers andemulsion polymerization prepared butadiene/acrylonitrile copolymers.

[0025] The commonly employed siliceous pigments which may be used in therubber compound include conventional pyrogenic and precipitatedsiliceous pigments (silica), although precipitated silicas arepreferred. The conventional siliceous pigments preferably employed inthis invention are precipitated silicas such as, for example, thoseobtained by the acidification of a soluble silicate, e.g., sodiumsilicate.

[0026] Such conventional silicas might be characterized, for example, byhaving a BET surface area, as measured using nitrogen gas, preferably inthe range of about 40 to about 600, and more usually in a range of about50 to about 300 square meters per gram. The BET method of measuringsurface area is described in the Journal of the American ChemicalSociety, Volume 60, Page 304 (1930).

[0027] The conventional silica may also be typically characterized byhaving a dibutylphthalate (DBP) absorption value in a range of about 100to about 400, and more usually about 150 to about 300.

[0028] The conventional silica might be expected to have an averageultimate particle size, for example, in the range of 0.01 to 0.05 micronas determined by the electron microscope, although the silica particlesmay be even smaller, or possibly larger, in size.

[0029] Various commercially available silicas may be used, such as, onlyfor example herein, and without limitation, silicas commerciallyavailable from PPG Industries under the Hi-Sil trademark withdesignations 210, 243, etc; silicas available from Rhodia, with, forexample, designations of Z1165 MP and Z165GR and silicas available fromDegussa AG with, for example, designations VN2 and VN3, etc.

[0030] Commonly employed carbon blacks can be used as a conventionalfiller. Representative examples of such carbon blacks include N110,N121, N220, N231, N234, N242, N293, N299, S315, N326, N330, M332, N339,N343, N347, N351, N358, N375, N539, N550, N582, N630, N642, N650, N683,N754, N762, N765, N774, N787, N907, N908, N990 and N991. These carbonblacks have iodine absorptions ranging from 9 to 145 g/kg and DBP numberranging from 34 to 150 cm³/100 g.

[0031] It may be preferred to have the rubber composition for use in thetire component to additionally contain a conventional sulfur containingorganosilicon compound. Examples of suitable sulfur containingorganosilicon compounds are of the formula:

Z-Alk-S_(n)-Alk-Z  I

[0032] in which Z is selected from the group consisting of

[0033] where R⁶ is an alkyl group of 1 to 4 carbon atoms, cyclohexyl orphenyl; R⁷ is alkoxy of 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8carbon atoms; Alk is a divalent hydrocarbon of 1 to 18 carbon atoms andn is an integer of 2 to 8.

[0034] Specific examples of sulfur containing organosilicon compoundswhich may be used in accordance with the present invention include:3,3′-bis(trimethoxysilylpropyl) disulfide, 3,3′-bis(triethoxysilylpropyl) disulfide, 3,3′-bis(triethoxysilylpropyl)tetrasulfide, 3,3′-bis(triethoxysilylpropyl) octasulfide,3,3′-bis(trimethoxysilylpropyl) tetrasulfide,2,2′-bis(triethoxysilylethyl) tetrasulfide,3,3′-bis(trimethoxysilylpropyl) trisulfide,3,3′-bis(triethoxysilylpropyl) trisulfide,3,3′-bis(tributoxysilylpropyl) disulfide,3,3′-bis(trimethoxysilylpropyl) hexasulfide,3,3′-bis(trimethoxysilylpropyl) octasulfide,3,3′-bis(trioctoxysilylpropyl) tetrasulfide,3,3′-bis(trihexoxysilylpropyl) disulfide,3,3′-bis(tri-2″-ethylhexoxysilylpropyl) trisulfide,3,3′-bis(triisooctoxysilylpropyl) tetrasulfide,3,3′-bis(tri-t-butoxysilylpropyl) disulfide, 2,2′-bis(methoxy diethoxysilyl ethyl) tetrasulfide, 2,2′-bis(tripropoxysilylethyl) pentasulfide,3,3′-bis(tricyclonexoxysilylpropyl) tetrasulfide,3,3′-bis(tricyclopentoxysilylpropyl) trisulfide,2,2′-bis(tri-2″-methylcyclohexoxysilylethyl) tetrasulfide,bis(trimethoxysilylmethyl) tetrasulfide, 3-methoxy ethoxy propoxysilyl3′-diethoxybutoxy-silylpropyltetrasulfide, 2,2′-bis(dimethylmethoxysilylethyl) disulfide, 2,2′-bis(dimethyl sec.butoxysilylethyl)trisulfide, 3,3′-bis(methyl butylethoxysilylpropyl) tetrasulfide,3,3′-bis(di t-butylmethoxysilylpropyl) tetrasulfide, 2,2′-bis(phenylmethyl methoxysilylethyl) trisulfide, 3,3′-bis(diphenylisopropoxysilylpropyl) tetrasulfide, 3,3′-bis(diphenylcyclohexoxysilylpropyl) disulfide, 3,3′-bis(dimethylethylmercaptosilylpropyl) tetrasulfide, 2,2′-bis(methyldimethoxysilylethyl) trisulfide, 2,2′-bis(methylethoxypropoxysilylethyl) tetrasulfide, 3,3′-bis(diethylmethoxysilylpropyl) tetrasulfide, 3,3′-bis(ethyl di-sec.butoxysilylpropyl) disulfide, 3,3′-bis(propyl diethoxysilylpropyl)disulfide, 3,3′-bis(butyl dimethoxysilylpropyl) trisulfide,3,3′-bis(phenyl dimethoxysilylpropyl) tetrasulfide, 3-phenylethoxybutoxysilyl 3′-trimethoxysilylpropyl tetrasulfide,4,4′-bis(trimethoxysilylbutyl) tetrasulfide,6,6′-bis(triethoxysilylhexyl) tetrasulfide,12,12′-bis(triisopropoxysilyl dodecyl) disulfide,18,18′-bis(trimethoxysilyloctadecyl) tetrasulfide,18,18′-bis(tripropoxysilyloctadecenyl) tetrasulfide,4,4′-bis(trimethoxysilyl-buten-2-yl) tetrasulfide,4,4′-bis(trimethoxysilylcyclohexylene) tetrasulfide,5,5′-bis(dimethoxymethylsilylpentyl) trisulfide,3,3′-bis(trimethoxysilyl-2-methylpropyl) tetrasulfide,3,3′-bis(dimethoxyphenylsilyl-2-methylpropyl) disulfide.

[0035] The preferred sulfur containing organosilicon compounds are the3,3′-bis(trimethoxy or triethoxy silylpropyl) sulfides. The mostpreferred compounds are 3,3′-bis(triethoxysilylpropyl) disulfide and3,3′-bis(triethoxysilylpropyl) tetrasulfide. Therefore as to formula I,preferably Z is

[0036] where R⁷ is an alkoxy of 2 to 4 carbon atoms, with 2 carbon atomsbeing particularly preferred; alk is a divalent hydrocarbon of 2 to 4carbon atoms with 3 carbon atoms being particularly preferred; and n isan integer of from 2 to 5 with 2 and 4 being particularly preferred.

[0037] The amount of the sulfur containing organosilicon compound offormula I in a rubber composition will vary depending on the level ofother additives that are used. Generally speaking, the amount of thecompound of formula I will range from 0.5 to 20 phr. Preferably, theamount will range from 1 to 10 phr.

[0038] It is readily understood by those having skill in the art thatthe rubber composition would be compounded by methods generally known inthe rubber compounding art, such as mixing the varioussulfur-vulcanizable constituent rubbers with various commonly usedadditive materials such as, for example, sulfur donors, curing aids,such as activators and retarders and processing additives, such as oils,resins including tackifying resins and plasticizers, fillers, pigments,fatty acid, zinc oxide, waxes, antioxidants and antiozonants andpeptizing agents. As known to those skilled in the art, depending on theintended use of the sulfur vulcanizable and sulfur-vulcanized material(rubbers), the additives mentioned above are selected and commonly usedin conventional amounts. Representative examples of sulfur donorsinclude elemental sulfur (free sulfur), an amine disulfide, polymericpolysulfide and sulfur olefin adducts. Preferably, thesulfur-vulcanizing agent is elemental sulfur. The sulfur-vulcanizingagent may be used in an amount ranging from 0.5 to 8 phr, with a rangeof from 1.5 to 6 phr being preferred. Typical amounts of tackifierresins, if used, comprise about 0.5 to about 10 phr, usually about 1 toabout 5 phr. Typical amounts of processing aids comprise about 1 toabout 50 phr. Such processing aids can include, for example, aromatic,naphthenic, and/or paraffinic processing oils. Typical amounts ofantioxidants comprise about 1 to about 5 phr. Representativeantioxidants may be, for example, diphenyl-p-phenylenediamine andothers, such as, for example, those disclosed in the Vanderbilt RubberHandbook (1978), Pages 344 through 346. Typical amounts of antiozonantscomprise about 1 to 5 phr. Typical amounts of fatty acids, if used,which can include stearic acid comprise about 0.5 to about 3 phr.Typical amounts of zinc oxide comprise about 2 to about 5 phr. Typicalamounts of waxes comprise about 1 to about 5 phr. Often microcrystallinewaxes are used. Typical amounts of peptizers comprise about 0.1 to about1 phr. Typical peptizers may be, for example, pentachlorothiophenol anddibenzamidodiphenyl disulfide.

[0039] Accelerators are used to control the time and/or temperaturerequired for vulcanization and to improve the properties of thevulcanizate. In one embodiment, a single accelerator system may be used,i.e., primary accelerator. The primary accelerator(s) may be used intotal amounts ranging from about 0.5 to about 4, preferably about 0.8 toabout 1.5, phr. In another embodiment, combinations of a primary and asecondary accelerator might be used with the secondary accelerator beingused in smaller amounts, such as from about 0.05 to about 3 phr, inorder to activate and to improve the properties of the vulcanizate.Combinations of these accelerators might be expected to produce asynergistic effect on the final properties and are somewhat better thanthose produced by use of either accelerator alone. In addition, delayedaction accelerators may be used which are not affected by normalprocessing temperatures but produce a satisfactory cure at ordinaryvulcanization temperatures. Vulcanization retarders might also be used.Suitable types of accelerators that may be used in the present inventionare amines, disulfides, guanidines, thioureas, thiazoles, thiurams,sulfenamides, dithiocarbamates and xanthates. Preferably, the primaryaccelerator is a sulfenamide. If a second accelerator is used, thesecondary accelerator is preferably a guanidine, dithiocarbamate orthiuram compound.

[0040] The mixing of the rubber composition can be accomplished bymethods known to those having skill in the rubber mixing art. Forexample the ingredients are typically mixed in at least two stages,namely at least one non-productive stage followed by a productive mixstage. The final curatives including sulfur vulcanizing agents aretypically mixed in the final stage which is conventionally called the“productive” mix stage in which the mixing typically occurs at atemperature, or ultimate temperature, lower than the mix temperature(s)than the preceding non-productive mix stage(s). The terms“non-productive” and “productive” mix stages are well known to thosehaving skill in the rubber mixing art. The rubber composition may besubjected to a thermomechanical mixing step. The thermomechanical mixingstep generally comprises a mechanical working in a mixer or extruder fora period of time suitable in order to produce a rubber temperaturebetween 140° C. and 190° C. The appropriate duration of thethermomechanical working varies as a function of the operatingconditions and the volume and nature of the components. For example, thethermomechanical working may be from 1 to 20 minutes.

[0041] Pneumatic tires are conventionally comprised of a generallytoroidal shaped casing with an outer circumferential tread adapted tothe ground contacting space beads and sidewalls extending radially fromand connecting the tread to the beads. The rubber composition may beincorporated in a variety of rubber components of the tire. For example,the rubber component may be a tread (including tread cap and treadbase), sidewall, apex, chafer, sidewall insert, wirecoat or innerliner.Preferably, the compound is a tread.

[0042] The pneumatic tire of the present invention may be a race tire,passenger tire, aircraft tire, agricultural, earthmover, off-the-road,truck tire and the like. Earthmover and off-the-road tires may alsogenerally be referred to as industrial tires. In one embodiment, thetire is a passenger or truck tire. The tire may also be a radial orbias, with a radial being preferred.

[0043] Vulcanization of the pneumatic tire of the present invention isgenerally carried out at conventional temperatures ranging from about100° C. to 200° C. Preferably, the vulcanization is conducted attemperatures ranging from about 110° C. to 180° C. Any of the usualvulcanization processes may be used such as heating in a press or mold,heating with superheated steam or hot air. Such tires can be built,shaped, molded and cured by various methods which are known and will bereadily apparent to those having skill in such art.

[0044] In one embodiment, the pneumatic tire is an agricultural orindustrial tire comprising a casing and a rubber tread disposed radiallyoutwardly of the casing, the tread having an inner tread and a pluralityof tread lugs projecting radially from the inner tread, the treadcomprising a vulcanizable rubber composition comprising, based on 100parts by weight of elastomer (phr),

[0045] (A) from about 30 to 100 phr of high trans random SBR comprisingfrom about 3 to about 30 percent by weight of styrene; and

[0046] (B) from about zero to about 70 phr of at least one additionalelastomer.

[0047] In the case of a agricultural or industrial tire, the typicalcure cycle for curing a green tire utilizes high temperatures and longercure times than is typical for smaller, passenger type tires. The longercure times and higher temperatures of cure are sufficient to cure thethick, heavy rubber components of the agricultural or industrial tire.These components include the tread lugs which typically cure more slowlythat the thinner parts of the tire. The tread lugs may have a width andlength in a range of from about 0.8 to about 2.75 inches, and a heightin a range of from about 1 to about 4 inches. The tread may further havea net-to-gross ratio in a range of from about 15 to about 40 percent asmeasured around the entire 360° circumference of a normally inflated andnormally loaded tire contacting a flat hard surface, as describedfurther hereinafter. As is known in the art, “Net-to-gross Ratio” meansthe ratio of the surface are of the normally loaded and normallyinflated tire tread rubber that makes contact with a hard flat surface,divided by the total area of the tread, including non-contactingportions such as grooves as measured around the entire circumference ofthe tire. Alternatively, the net-to-gross ratio may be in a range offrom about 15 to about 30 percent. Thus, the cure cycle of hightemperature and long time would be understood by one skilled in the artas characteristic of cure in an agricultural or industrial tire havingthick, heavy tread lugs.

[0048] In one embodiment, the agricultural or industrial tire may becured at a temperature ranging from about 160° C. to about 190° C. Inanother embodiment, the agricultural tire may be cured at a temperatureranging from about 160° C. to about 180° C. The agricultural tire may becured for a time ranging from about 40 minutes to about 150 minutes. Inanother embodiment, the agricultural tire may be cured for a timeranging from about 60 minutes to about 120 minutes. Generally, the curetime and temperature is sufficient to cure the characteristically thick,heavy tread of the agricultural or industrial tire. The agricultural orindustrial tire having thick, heavy tread is characteristically curedusing the long times and high temperatures.

[0049] The following examples are presented for the purposes ofillustrating and not limiting the present invention. All parts are partsby weight unless specifically identified otherwise.

EXAMPLE I

[0050] In this example, a series of high trans random solution SBR(HTSBR) polymers prepared following the teachings of U.S. applicationSer. No. 10/124,006, now U.S. Pat. No. 6,627,715, were compounded andtested for various physical properties. These polymers are characterizedas indicated in Table 1.

[0051] The polymers were compounded with 60 phr of HTSBR and 40 phr ofnatural rubber (NR), and with standard amounts of conventional curativesand processing aids as indicated in Table 2, and cured with a standardcure cycle. Cured samples were evaluated for various physical propertiesfollowing standard tests protocols as indicated in Table 3. TABLE 1Sample 1 2 3 4 5 6 7 8 Styrene (%) 3.7 5.8 8.3 10.6 12.9 21.5 27.4 37.9Trans 1,4 77.2 75 74.5 73 69.7 64.2 59.6 50.8 PBD (%) Cis 1,4- 14.7 1513.3 13.3 13.3 11.2 10.3 8.8 PBD (%) 1,2 PBD (%) 4.4 4.2 3.9 3.1 4.1 3.12.7 2.5 T_(g) −81.4 −79.8 −76.8 −77 −77 −66.2 −58 −49 T_(m) 13 12 12 183 −3 — —

[0052] TABLE 2 Standard Compound Recipe Natural Rubber 40 HTSBR 60 ZincOxide 5 Process Oil 12.5 Stearic Acid 2.5 Wax 1.5 Carbon Black 50 Sulfur1.50 Antidegradants¹ 2.75 Accelerators² 1

[0053] TABLE 3 Sample 1 2 3 4 5 6 7 8 Peel Strength, N Peel at 23° C.366.7 345.2 373.9 285.1 146.4 202.8 111.1 82.9 Peel at 95° C. 137.5242.6 216 214.8 57.8 88 151.2 76.2 Stress-Strain Modulus 300% (MPa) 3.725.93 3.49 5.56 3.4 3.44 5 3.7 Tensile (MPa) 17.5 22.2 19.8 23.4 17.718.1 20.4 16.8 Elongation (%) 749 644 784 644 792 757 693 725 ZwickRebound 23° C. 42.4 44.4 41.8 46 37.2 37.6 34.2 27.8 100° C. 50.4 55.250.8 57.8 45.2 47.2 46.4 41.8 DIN Abrasion Loss 68 63 67 71 74 82 97 119(gm/cc)

EXAMPLE II

[0054] In this example, a trans solution SBR (HTSBR) polymer preparedfollowing the teachings of U.S. application Ser. No. 10/124,006, nowU.S. Pat. No. 6,627,715, were compounded and tested for various physicalproperties, and compared with a commercially available emulsion SBR(ESBR).

[0055] The polymers were compounded at 100 phr of the polymer withstandard amounts of conventional curatives and processing aids asindicated in Table 4, and cured using a standard cure cycle. Curedsamples were evaluated for various physical properties followingstandard test protocols as indicated in Table 5. TABLE 4 Compound Recipe(Parts by Weight) Sample 9 10 Trans SBR³ 100 0 Emulsion SBR⁴ 0 100Carbon Black 50 50 Processing Oil 12.5 12.5 Antidegradants¹ 0.75 0.75Stearic Acid 2.5 2.5 Zinc Oxide 5 5 Sulfur 1.5 1.5 Accelerators² 0.9 0.9

[0056] TABLE 5 Compound Physical Properties Sample 9 10 Stress-StrainTensile Strength (MPa) 14.2 10.3 Elongation at break (%) 513 421 300%modulus (MPa) 5.4 6.2 Zwick Rebound  23° C. (%) 48 43 100° C. (%) 52 50Peel Strength @ 95° C., N 284 161 DIN Abrasion Loss 59 78 (gm/cc)

[0057] The samples demonstrate the unexpectedly superior tear, rebound,and abrasion properties obtained for the HTSBR samples. This isparticularly surprising, since generally improvements in tear strengthare realized only with a compromise in rebound and abrasion, and viceversa. Further, the tear values for the lower styrene content aresurprisingly high. For example, the tear (peel) strength values at 23°C. and 95° C. for Samples 1, 2, 3, and 4 having styrene contents in arange of about 3 to about 11 percent are significantly higher than thetear values for Samples 6 through 8 having styrene contents of greaterthan 20 percent. In addition, the room temperature and 100° C. reboundvalues for the samples having lower styrene contents are superior tothose for the samples with higher styrene contents. DIN abrasion for thelow styrene content samples is also significantly greater than for thehigher styrene content samples.

EXAMPLE III

[0058] In this example, a trans solution SBR (HTSBR) polymer preparedfollowing the teachings of U.S. application Ser. No. 10/124,006, nowU.S. Pat. No. 6,627,715, were compounded using a typical tread recipefor an agricultural or industrial tire and tested for various physicalproperties, and compared with a commercially available emulsion SBR(ESBR).

[0059] The polymers were compounded at 100 phr of the polymer withstandard amounts of conventional curatives and processing aids asindicated in Table 6, and cured using a standard cure cycle. Curedsamples were evaluated for various physical properties followingstandard test protocols as indicated in Table 7. TABLE 6 Compound Recipe(Parts by Weight) Sample No. 11 12 E-SBR 85 0 HTSBR 0 85 Natural Rubber15 15 Carbon Black 65 65 Aromatic process oil 19 16 Sulfur 1.65 1.90

[0060] TABLE 7 Compound Physical Properties Sample No. 11 12 RingTensile (ASTM D412), Cured 74 min at 160° C. 100% Modulus (MPa) 1.481.36 300% Modulus (MPa) 6.22 6.16 Modulus Ratio (300/100) 4.20 4.53Break Str (MPa) 14.51 13.59 % Elongation 578 529 Shore A Hardness (ASTMD2240), Cured 74 min at 160° C. Hardness @ RT 68.7 65.9 Hardness @ 100°C. 52.8 54.8 Zwick Rebound (ASTM 1054), Cured 74 min at 160° C. Rebound@ RT 31.3 36.9 Rebound @ 100° C. 40.1 40.8 Ring Tensile (ASTM D412),Cured 74 min at 160° C., Aging: 3 days at 90° C. in Air 100% Modulus(MPa) 2.03 2.11 300% Modulus (MPa) 8.59 10.37 Modulus Ratio (300/100)4.23 4.91 Break Str (MPa) 13.4 14.12 % Elongation 473 412 Shore AHardness (ASTM D2240), Cured 74 min at 160° C., Aging: 3 days at 90° C.in Air Hardness @ RT 72.5 71 Hardness @ 100° C. 57.4 60.6 Zwick Rebound(ASTM 1054), Cured 74 min at 160° C., Aging: 3 days at 90° C. in AirRebound @ RT 32.6 39.7 Rebound @ 100° C. 42 45.1 RPA, 150° C. CureUncured G′ (15%, 100° C., .83 Hz) 142 212 T′02 (min.) 1.44 1.41 T′25(min.) 7.86 5.59 T′90 (min.) 21.00 13.67 G′ (1%, 100 C, 1 Hz) 1732 1923G′ (10%, 100 C, 1 Hz) 939 1159 G′ (50%, 100 C, 1 Hz) 644 807 TanD (10%,100 C, 1 Hz) 0.206 0.182 RPA, 191° C. Cure Uncured G′ (15%, 100° C., .83Hz) 146 218 T′02 (min.) 1.68 1.57 T′25 (min.) 2.07 1.87 T′90 (min.) 3.262.55 G′ (1%, 100 C, 1 Hz) 1642 1668 G′ (10%, 100 C, 1 Hz) 819 908 G′(15%, 100 C, 1 Hz) 731 817 G′ (50%, 100 C, 1 Hz) 495 552 TanD (10%, 100C, 1 Hz) 0.256 0.257 Instron Tear (ASTM D624), Cured 74 + 5 min at 160°C. Avg Load (N) 343 399 Energy (N-cm) 5222 6078 Avg Peak Load (N) 350447 SD of Energy Btwn Limits 0.51 3.33 (1 = knotty, 5 = smooth) 1 1Instron Tear (ASTM D624), Cured 74 + 5 min at 160° C., Aging: 3 days at90° C. in Air Avg. Load (N) 325 407 Energy (N-cm) 6648 8330 Avg. PeakLoad (N) 343 449 SD of Energy Btwn Limits 0.61 9.22 (1 = knotty, 5 =smooth) 3 2 DIN Abrasion (ASTM D5963, 10 N force), Cured 74 min at 160°C. Rel. Volume Loss (g) 126 76 Room Temp Peel Strength, To Self, Cured74 min at 160° C. SS-AVG.-LOAD (N) 154.45 161.61 (1 = knotty, 5 =smooth) 5 3 RT Peel Strength, To Self, Cured 74 min at 160° C., Aging: 3days at 90° C. in Air SS-AVG-LOAD (N) 121.64 127.32 (1 = knotty, 5 =smooth) 5 3 Rheometer, ODR, 150° C. Max Torque (dNm) 28.28 35.16 MinTorque (dNm) 5.96 9.39 TS1 (min) 6.18 4.14 T25 (min) 9.59 6.38 T90 (min)24.46 13.35 Delta Torque (dNm) 22.32 25.77 tR2 71.12 Final Torque 27.8331.94 Rev = (Max − Final) 0.45 3.22 Reversion Rate (dNm/120′) = Rev/0.57 3.62 (120 − T90) * 120

[0061] Modern agricultural or industrial tire utilization requires acool running tread, despite the extremely thick lug design, to enableextended running periods over paved roads at maximum speed, which isabout 30 kilometers per hour, four times the normal speed in the field.Use of the HTSBR polymer in agricultural and industrial treads willprovide reduced running temperature over the road with equivalentresistance to stubble and damage resistance in the field. The data oftables 6 and 7 show equivalent tear strength, better abrasionresistance, and better rebound compared to an emulsion SBR. The curestate can be altered to achieve an improvement in tear strength, yetequivalent abrasion and rebound.

[0062] The composition is especially useful for a radial rear farm tiretread, especially on the new high horse-power tractors, where coolrunning temperature is needed over the road in addition to superiorresistance to stubble damage in the field.

[0063] While certain representative embodiments and details have beenshown for the purpose of illustrating the subject invention, it will beapparent to those skilled in this art that various changes andmodifications can be made therein without departing from the scope ofthe subject invention.

What is claimed is:
 1. An agricultural or industrial tire comprising acasing and a rubber tread disposed radially outwardly of the casing, thetread having an inner tread and a plurality of tread lugs projectingradially from the inner tread, the tread comprising a vulcanizablerubber composition comprising, based on 100 parts by weight of elastomer(phr), (A) from about 30 to 100 phr of high trans random SBR comprisingfrom about 3 to about 30 percent by weight of styrene and a trans 1,4butadiene content in the polybutadiene segments of the SBR of greaterthan 60 percent by weight, wherein said high trans random SBR isproduced by a process that comprises copolymerizing styrene and1,3-butadiene in an organic solvent in the presence of a catalyst systemthat is comprised of (i) an organolithium compound, (ii) a group IIametal salt selected from the group consisting of group IIa metal saltsof amino glycols and group IIa metal salts of glycol ethers, and (iii)an organometallic compound selected from the group consisting oforganoaluminum compounds and organomagnesium compounds; and (B) fromabout zero to about 70 phr of at least one additional elastomer.
 2. Theagricultural or industrial tire of claim 1, wherein said vulcanizablerubber composition comprises from about 50 to about 100 phr of hightrans random SBR comprising from about 3 to about 30 percent by weightof styrene, and from about 10 to about 50 phr of at least one additionalelastomer.
 3. The agricultural or industrial tire of claim 1, whereinsaid high trans random SBR comprises from about 3 to about 20 percent byweight of styrene.
 4. The agricultural or industrial tire of claim 1,wherein said high trans random SBR comprises from about 3 to about 10percent by weight of styrene.
 5. The agricultural or industrial tire ofclaim 1, wherein said high trans random SBR has a trans content ofgreater than 70 percent by weight.
 6. The agricultural or industrialtire of claim 1, wherein said high trans random SBR has a glasstransition temperature in a range of from about −55° C. to about −85° C.7. The agricultural or industrial tire of claim 1, wherein saidcomponent is selected from the group consisting of tread cap, treadbase, sidewall, apex, chafer, sidewall insert, wirecoat and innerliner.8. The agricultural or industrial tire of claim 1, wherein saidcomponent is a tread cap or tread base.
 9. The agricultural orindustrial tire of claim 1, wherein said at least one additionalelastomer is selected from the group consisting of cis 1,4-polyisoprenerubber (natural or synthetic, although natural is preferred),3,4-polyisoprene rubber, styrene/isoprene/butadiene rubber,styrene/isoprene rubber, emulsion and solution polymerization derivedstyrene/butadiene rubbers, cis 1,4-polybutadiene rubbers and emulsionpolymerization prepared butadiene/acrylonitrile copolymers.
 10. Theagricultural or industrial tire of claim 1, wherein said at least oneadditional elastomer is natural rubber.
 11. The agricultural orindustrial tire of claim 1, wherein said vulcanizable rubber compositionfurther comprises from about 20 to about 100 phr of carbon black. 12.The agricultural or industrial tire of claim 1, wherein saidvulcanizable rubber composition further comprises from about 20 to about100 phr of silica.
 13. The agricultural or industrial tire of claim 1,wherein less than 10 percent of the total quantity of repeat unitsderived from styrene in said high trans random SBR are in blockscontaining more than five styrene repeat units.
 14. The agricultural orindustrial tire of claim 1, wherein less than 4 percent of the totalquantity of repeat units derived from styrene in said high trans randomSBR are in blocks containing 5 or more styrene repeat units.
 15. Theagricultural or industrial tire of claim 1, wherein less than 1 percentof the total quantity of repeat units derived from styrene in said hightrans random SBR are in blocks containing 5 or more styrene repeatunits.
 16. The agricultural or industrial tire of claim 1, wherein saidhigh trans random SBR is produced by a process that comprisescopolymerizing styrene and 1,3-butadiene in an organic solvent in of acatalyst system that is comprised of (A) an organolithium compound, (B)a group IIa metal salt of an amino glycol, and (C) an organometalliccompound selected from the group consisting of organoaluminum compoundscontaining less than 13 carbon atoms and organomagnesium compounds. 17.The agricultural or industrial tire of claim 1, wherein each lug has awidth and length in a range of from about 0.8 to about 2.75 inches, anda height in a range of from about 1 to about 4 inches, and wherein thetread has a net-to-gross ratio in a range of from about 15 to about 40percent as measured around the entire 360° circumference of a normallyinflated and normally loaded tire contacting a flat hard surface. 18.The agricultural or industrial tire of claim 1, wherein said lugscomprise said composition.